This video and project was featured on Solarbotics.com on 8/26/2011.
I really enjoy making solar powered machines and BEAM Robots. With a good source of light they are self reliant. A Pummer is a solar powered self activating LED flasher. Pummers are a fun non-moving branch of BEAM Robotics. They are nocturnal techno "plants" that soak up sunlight during the daytime, then get active at night. Their nocturnal activity consists of a blinking light with a soft turn off, which means that it turns on fast and bright, but slowly fades away and then repeats. This makes a great project, gift, desk toy... I have mine on an end table and the light from the lamp is enough to make it blink all night.
(See the Duel LED Pummer video in step 7)
Step 1: Items Needed
1 - >3V Solar Cell (Solarbotics $8)
1 - 74AC240 Microchip (The Bicore) (Solarbotics $1)
1 - Diode (Solarbotics $0.10 or RadioShack 2 for $1.19)
1 - LED (any color and size you want) (Solarbotics $1.10 or RadioShack $1.69)
2 - 0.22µF Capacitors (code 224) (Solarbotics $0.80 or RadioShack $1.59)
1 - 1000µF Capacitor (Solarbotics $0.80 or RadioShack $1.29)
1 - 4.7M Resister (I used 5.1M) (Solarbotics $0.20 or RadioShack 5 pack of 1M $1.19)
1 - 100K Resister (Solarbotics $0.20 or RadioShack 5 pack $1.19)
1 - 1K Resister (Solarbotics $0.20 or RadioShack 5 pack $1.19)
1 - 2 AA Battery Holder with Wire Leads (Solarbotics $2.75 or RadioShack $1.99)
2 - AA Rechargeable Ni-Cd Batteries (RadioShack UltraLast® 1.2V/700mAh Ni-Cd "AA" Batteries (4-Pack) $9.99)
You can be creative and use your imagination to make it into anything you want, but this is what I used to make my Techno Flower:
1 - Hard-Drive Platter
1 - Floppy Disk Drive Magnet Coil
2 - Remote Control Circuit Boards
1 - Large Phone Keypad Circuit Board for Base
Read Step 7 for ideas on changing the parts if you can't find the right type.
Step 2: Free-form the Bicore
Numbering the Chip's Legs:
-Refer to the picture diagram.
Hold the 74AC240 Chip and carefully bend the legs to match the pictures:
-This can be done many different ways, but this is how i did it.
-Bend up Legs 5, 7, 9, 11, 13, 15, and 18.
-Bend Legs 1 and 19 up and over the top so they are touching.
-Bend out Legs 10, 17 and 20.
Solder leads/wire to legs:
(For example, 5-7-9, solder one wire across the three legs 5, 7, and 9 so they are all connected.)
Step 3: Add Components to the Bicore
-Add the .22µF Capacitors , you can solder one on legs 2, 3 and the other on legs 17, 18.
-Add the Diode to the front end. Cut the leads short and solder them to legs 1 and 20. The band should be near the leg 20 side. Something that helps me (because I often forget) is that when looking at a diode symbol the line is the cathode (negative end). The line on the symbol should match the line on the diode and the flat side of the LED. :-)
-Add the 4.7M Resistor . Cut the leads short and attach it to the bottom side between Leg 2 and 17.
-Add the 1000µF Capacitor . Solder the cathode (the side with the bar or the side the arrow is pointing too) to Leg 12.
-Now there are 2 things soldered to the 1000µF anode: the anode of the LED and one side of the 1K resistor .
-The other lead of the LED (the cathode-the flat side) is soldered to Leg 9.
-Solder a wire from the end of the 1K resistor to Leg 20. This will also be attached to the positive side of the battery.
Step 4: The Power!
-For now don't put the batteries in the holder.
-You want to find the positive and negative solder points on the Solar Cell . If it's not labeled you can use a multimeter to find out which is which.
-Solder the 100K Resistor to the positive and negative.
-Then from the negative side solder on a short wire (black if you have it) and solder it to the black wire from the battery holder and to the Leg 10 on the chip. You may have to add a black wire to the Leg 10 on the chip to attach it to the others. So you now have 3 black (negative, ground) wires all coming together. On the schematic, ground is the symbol of 3 parallel lines in the shape of an arrow pointing down.
-Next you will attach the positive (the plus signs on the schematic) together. You may have already attached a wire from Pin 20 to the end of you 1K Resistor, so if not do that now and then also attach the red wire from the battery to the same end of the 1K Resistor.
-Almost done! Now just run a wire from the positive side of the solar cell to the pin bridge you made with Pins 1 and 19.
-Put the 2 Batteries in, make sure the solar cell is covered and your LED should be Pumming! Then uncover the solar cell and face it to a light to see if the LED stops lighting.
Step 5: Making the Flower
Making the Flower:
-Yours will be unique!
-Extend the wires from the LED so you can place it where you want it.
-Make sure you position the Solar Cell so it faces where the sun/desk light will be coming from.
-I used hot glue to hold it all together.
-The battery holder can be used as a base and support for the stem. (see video at the top)
-You may need to scratch up the back of the hard drive platter where you want to glue to help it hold.
Step 6: Troubleshooting
-Double check that the chip, LED, capacitor, and diode are in the right way.
-Double check all your solder connections.
-Never at any time attach this circuit to a voltage supply of greater than 6V, this will fry the chip.
-If you have a multimeter, check that there is some voltage in the batteries. Minimal operation is around 1.4V, depending on the voltage needed to power the LED (white or blue LED’s may need about 2.0V).
-The pummer will not turn on until the light level is below the set threshold. If you want to force it on, either short circuit the solar cell or short circuit the 100K resistor.
-In this circuit, the frequency must be slow enough that the 1000µF cap is able to fully charge between illuminations. Generally, the pummer should not flash more than once a second. If you want a faster flash rate, try using the other single LED pummer.
-Hopefully with all the pictures you should be able to follow along. You can leave questions in the comments section and I'll try my best to answer them :-)
Step 7: Tips, Fun Changes, and Useful Advice
-If you want to try it out, here is a circuit for a Dual LED Pummer (See my new video below). Only LED 2 will see the voltage doubling effect so LED 1 must operate at or below 2.4V to actually light up (green, red or yellow should be fine). It is the same as before except for this don't have the 1K Resistor and has an extra LED put with the original LED but flipped around. (see, Dual LED Pummer schematic and video below)
-A single LED lower efficiency pummer operates down to lower voltages and can be run at high frequencies to make a flashlight. The disadvantage being that there are high current spikes when the LED flashes and when the capacitor charges, leading to wasted current, and shortened battery life. (See, Single LED Lower Efficiency Pummer schematic)
-Playing with the resistors: By raising the value of the 100K resistor tying the enables to ground, the pummer will wait until it gets darker to turn on. By raising the 4.7M resistor, the pummer will flash slower but with more powerful bursts.
-If you want a really efficient long lasting pummer, replace the 74AC240 with a 74HCT240, and slow the frequency way down. Run only one LED and replace the 1K resistor with a 4.7K resistor. That should run a week or two off of a single charge!
-We have experimented with different power storage devices and to date, the Ni-Cd batteries still come out on top. A close second is a large 10F 2.5V gold cap. I have some pummers built with AAA Ni-Cds that are still working after 4 years of operation.
-Pummers can live outdoors. The limiting factor is the temperature range that the power-storage device will operate at. It is feasible to have a post-mounted pummer on the side of a road in the middle of winter, if you bury the battery underground to protect it from getting too cold. If you do want to try this, you must also waterproof the pummer by potting it or sealing it in a container.
-An outdoor test pummer using Ni-Cds has been running two years, and survives temperature extremes from -30 deg C to +30 deg C. So far, so good!
-You may want to put the LED on a long neck. This is to get the LED visible above a window ledge.
Step 8: For More Information
(Big thanks to Solarbotics.com! Not only for the awesome website, cool products, and friendly staff, but for giving permission to use their schematics, info, and featuring my project on their site on 8/26/2011.)
My YouTube Videos :-) GeekGuyMJ